Catalyst and method for the synthesis of chlorine dioxide, and method of making catalyst for the synthesis of chlorine dioxide

ABSTRACT

Chlorine dioxide is generated from an aqueous solution of sodium chlorite in the presence of a catalyst having a reduced rate of deactivation. The catalyst is preferably palladium, or palladium together with another platinum group metal (e.g., Pd+Pt), or palladium together with a Group IB metal (e.g., Pd+Au) deposited on a support modified by Group IA carbonate salt (e.g., K 2 CO 3 ) or a Group IIA carbonate salt (e.g., CaCO 3 ) or a magnesium salt that can be converted to MgO or a support consisting of a Group IA carbonate salt or a Group IIA carbonate salt or a magnesium salt that can be converted to MgO.

BACKGROUND TO THE INVENTION

[0001] The present invention relates to a catalyst for the synthesis ofchlorine dioxide and to a method of making such a catalyst. The catalystis preferably palladium, or palladium together with another platinumgroup metal (e.g., Pd+Pt), or palladium together with a Group IB metal(e.g., Pd+Au) deposited on a support consisting of a Group IA carbonatesalt (e.g., K₂CO₃) or a Group IIA carbonate salt (e.g., CaCO₃) or amagnesium salt that can be converted to MgO or a support modified byGroup IA carbonate salt (e.g., K₂CO₃) or a Group IIA carbonate salt(e.g., CaCO₃) or a magnesium salt that can be converted to MgO. Thecatalysts of the present invention has a slower rate of deactivationthan catalysts previously used for this purpose.

[0002] In another aspect, the present invention concerns a method forgenerating chlorine dioxide from an aqueous solution of a precursortherefor and directing the resulting chlorine dioxide at the material tobe disinfected.

[0003] Chlorine dioxide is known to act as a disinfecting or sterilizingagent for solutions and devices (e.g., contact lenses). Chlorine dioxideis generally produced from a solution of a chlorine dioxide precursor,such as sodium chlorite solutions, by contacting the solution with acatalyst (e.g., catalysts containing noble metals, as described forexample in U.S. Pat. No. 5,008,096). However, known catalysts have thedisadvantage of becoming greatly deactivated within a matter of days.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide novel chlorinedioxide generating catalysts having a slower rate of deactivation thanknown catalysts. In achieving the above and other objects, one featureof the invention resides in a catalyst which is composed of a supportwherein the outside edge of the support is impregnated with palladium orpalladium and another platinum group metal or palladium and a Group IBmetal. The support itself is selected from the group of supportsmodified by a Group IA carbonate salt or a Group IIA carbonate salt or amagnesium salt that can be converted to MgO. Many well known catalystsupports, such as gamma alumina, can be used to form the modifiedsupport as described. In another aspect, the Group IA carbonate salt(e.g., K₂CO₃) or Group IIA carbonate salt (e.g., CaCO₃) or a magnesiumsalt that can be converted to MgO can be formed into a self sustainingsupport such as a pellet or honeycomb.

[0005] Another object of the present invention is to provide a method ofmaking a catalyst for producing chlorine dioxide having a slower rate ofdeactivation. The method involves preadjusting the pH of an aqueoussolution of a palladium or palladium and another platinum group metal orpalladium and a Group IB metal salt to a pH range of 1 to 6.3, addingthe solution to a slurry of water and a support selected from supportsmodified by a Group IA carbonate salt or a Group IIA carbonate salt or amagnesium salt that can be converted to MgO or a support consisting of aGroup IA carbonate salt (e.g., K₂CO₃) or a Group IIA carbonate salt(e.g., CaCO₃) or a magnesium salt that can be converted to MgO,maintaining the pH of the slurry from 6 to 10 for several minutes at atemperature of 70° to 90° C., and adding a reducing agent, therebyimpregnating the outside edge of the support with palladium or palladiumand another platinum group metal or palladium and a Group IB metal.

[0006] An additional object of the present invention is to provide amethod for generating chlorine dioxide from a chlorine dioxideprecursor. The method involves contacting an aqueous medium containing achlorine dioxide precursor with the above described catalyst.

[0007] Another method for generating chlorine dioxide from a chlorinedioxide precursor involves providing a multicompartment container, afirst compartment containing a chlorine dioxide precursor, a secondcompartment containing the catalyst described above, dispelling from thefirst compartment a quantity of the chlorine dioxide precursor to flowinto the second compartment containing the catalyst, contacting theprecursor with the catalyst thereby forming chlorine dioxide, andejecting the chlorine dioxide from the container to the surface of anitem to be disinfected or treated.

[0008] Furthermore, there is provides a two component package comprisingthe catalyst described above and a chlorine dioxide precursor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be further understood with referenceto the drawings, wherein:

[0010]FIG. 1 is a graph of the effect of alloying Pd with Au, Ag or Pton catalyst deactivation;

[0011]FIG. 2 is a graph of the effect of the support on Pd/Au catalysts;

[0012]FIG. 3 is a graph of the effect of the support on Pd/Pt catalysts;

[0013]FIG. 4 is a graph of the effect of the support on Pd catalysts;and

[0014]FIG. 5 is a schematic drawing of a multicompartment containerwhich contains chlorine dioxide precursor and the catalyst whichgenerates chlorine dioxide from the precursor.

[0015]FIG. 6 is a graph of the performance of a Pd/Au catalyst on aK₂CO₃ modified alumina support.

DETAILED DESCRIPTION OF THE INVENTION

[0016] A catalyst made for the generation of chlorine dioxide inaccordance with this invention is comprised of palladium, or palladiumtogether with another platinum group metal (e.g., Pd+Pt), or palladiumtogether with a Group IB metal (e.g., Pd+Au) deposited on a supportmodified by Group IA carbonate salt (e.g., K₂CO₃) or a Group IIAcarbonate salt (e.g., CaCO₃) or a water soluble magnesium salt (e.g.,acetate, nitrate, carbonate, chloride) that can be converted to Mgo or asupport consisting of a Group IA carbonate salt (e.g., K₂CO₃) or a GroupIIA carbonate salt (e.g., CaCO₃) or a water soluble magnesium salt(e.g., acetate, nitrate, carbonate, chloride) that can be converted toMgO. The catalytic metal must be present at a weight % of at least 0.1and up to 20, preferably 1 to 10, based on the total weight of thecatalyst. Palladium is preferred. Aqueous solutions of Group VIII andGroup IB metal salts (i.e., halides and nitrates) can be used in thepreparation of the catalyst. For example, the following ranges (wt/wt)can be used: ratio of Au to Pd, 0.01:1 to 2:1, preferably 0.2:1 to0.8:1; ratio of Pt to Pd, 0.01:1 to 2:1, preferably 0.2:1 to 0.8:1.

[0017] The support, which is modified by Group IA carbonate salt (e.g.,K₂CO₃) or a Group IIA carbonate salt (e.g., CaCO₃) or a magnesium saltthat can be converted to MgO, may be selected from many well known highsurface metallic or ceramic catalyst supports, such as gamma alumina,silica-alumina, silica, titania, etc. Typically, such supports have asurface area of at least about 40 m²/g, preferably 100 m²/g.*

[0018] The method of making the catalyst is illustrated with palladium,but other platinum group metals or combinations of palladium and anotherplatinum group metal (e.g., Pd+Pt) or combinations of palladium and aGroup IB metal (e.g., Pd+Au) can be substituted with comparable results.The catalyst is supported for example on a MgO or CaCO₃ or K₂CO₃catalyst support or matrix which is substantially inert when exposed tothe conditions used in the enhanced generation of chlorine dioxide froma chlorine dioxide precursor in accordance with the present invention.The support must be thermostable and must provide high support area. Theconfiguration of supports are known in the art. The supported componentmay have any suitable shape or configuration, such as sheets, rods,extrudates, tablets, pills, irregular shaped particles, spheres, disks,pellets and the like. Monoliths can also be used. The formation of theMgO or CaCO₃ or K₂CO₃ inert support can be carried out by known means.

[0019] Any of a number of conventional techniques can be employed todeposit the platinum group metal(s), or platinum group metal and GroupIB metal, on the support material. These techniques includeimpregnation, co-precipitation, ion-exchange, dipping, spraying, vacuumdeposits and the like.

[0020] The palladium or palladium and another platinum group metal(e.g., Pd+Pt) or palladium and a Group IB metal (e.g., Pd+Au) can bedeposited on the outside edge of the MgO or CaCO₃ or K₂CO₃ support in anumber of ways known in the art. The preferred method is by promotingrapid hydrolysis of the water soluble salts of the noble metals whenadded to a MgO or CaCO₃ or K₂CO₃ particulate-water slurry. This can beachieved by preadjusting the pH of the noble metal salt solution to 1 to6.3, depending on the metal salts used, prior to addition to the slurry.The concentration of the noble metal salt in the aqueous solution is notcritical and can vary widely. After that, the process is continued bymaintaining the pH of the slurry at 6 to 10 for several minutes at atemperature of 70° to 90° C., prior to the addition of a reducing agent.

[0021] The result of following these reaction conditions is that thefinely divided MgO or CaCO₃ or K₂CO₃ particles have the catalyticallyactive metal, e.g., palladium (or Pd+Pt or Pd+Au), deposited on theexterior surface of the particle. The MgO or CaCO₃ or K₂CO₃ particle canrange from 0.01 to 4 mm in size, preferably 0.3 to 4 mm, though theupper limit is not critical. The penetration of the palladium (or Pd+Ptor Pd+Au) into the MgO or CaCO₃ or K₂CO₃ particle can be determined bytransmission electron microscopy.

[0022] Broadly, the method for enhancing generation of chlorine dioxideaccording to the present invention involves contacting an aqueous mediumcontaining a chlorine dioxide precursor with a catalyst formed of Pd (orPd+Pt or Pd+Au) deposited on a MgO or CaCO₃ or K₂CO₃ inert support. Thetemperature at which the aqueous medium is maintained during contact ofthe chlorine dioxide precursor with the catalyst can vary widely.Preferably, the temperature is in the range of 5° C. to 80° C., andpreferably 5° C. to 50° C. Typically the process is carried out atambient temperature. The pH of the aqueous medium is usually in therange of 1 to 8, preferably 4 to 8. Generally, the catalyst contact timewith the chlorine dioxide precursor ranges from 0.01 to 20 seconds.

[0023] Chlorine dioxide precursors which may be employed in the practiceof the present invention are those compounds capable of generating,releasing or being converted to chlorine dioxide when contacted with acatalyst formed of Pd (or Pd+Pt or Pd+Au) deposited on a MgO or CaCO₃ orK₂CO₃ support under the reaction conditions previously described. Anymetal chlorite salt capable of generating chlorine dioxide can beutilized as the chlorine dioxide precursor. Preferably, alkali metalchlorites are used, especially sodium chlorite in an aqueous medium. Theamount of chlorine dioxide precursor present in the aqueous medium canvary widely and will be dependent upon the amount of chlorine dioxide tobe generated. For example, it has been found that the amounts ofchlorine dioxide precursor present in the aqueous medium can range from0.0001 to 30 weight %, preferably 0.0005 to 10 weight %. Preferably, achlorine dioxide complex sold by Bio-Cide International, Inc. of Norman,Okla. under the trademark Purogene^(R), is used (described in U.S. Pat.No. 5,008,096, incorporated by reference in its entirety).

[0024] In order to be able to control the chlorine dioxide formed in thecourse of the catalytic reaction and to direct the flow of the chlorinedioxide, it is desirable to conduct the reaction in a space where thecatalyst and precursor solution are kept separate until it is desired togenerate the chlorine dioxide. Thus, for marketing the product, a twocomponent package can be provided with suitable separation means anddispenser means to direct the flow of chlorine dioxide to the surface,object or material to be disinfected.

[0025] All kinds of contact lenses may be disinfected by utilizingchlorine dioxide produced by the catalysts of the present invention in amanner known in the art.

[0026] In accordance with a further embodiment of the present inventionthere is provided a two component package which separately contains thecatalyst and the chlorine dioxide precursor.

[0027] As shown in FIG. 5, there can be provided a device for dispensingchlorine dioxide 10 containing a compartment 12 for holding the aqueousprecursor. The device also has a compartment 20 for holding the catalyst14 separate and apart from the aqueous precursor. A tube or other device16 is arranged so as to permit contact of the aqueous precursor with thecatalyst. A dispenser of any convenient design 18 can be arranged in thedevice 10 for delivery of the chlorine dioxide generated in the uppercompartment 20.

[0028] Furthermore, the present invention concerns a method forgenerating chlorine dioxide from a chlorine dioxide precursor whichutilizes the multicompartment container shown in FIG. 5. In order togenerate chlorine dioxide, the container, for example, can be invertedand the compartment containing the chlorine dioxide precursor issqueezed in order to flow at least a portion of the chlorine dioxideprecursor into the compartment which contains the catalyst. Theresulting chlorine dioxide is ejected from the container via an openingto the surface of the item (e.g., contact lenses) to be disinfected ortreated. The compartment which contains the catalyst is separated fromthe compartment containing the chlorine dioxide precursor by a catalystretention means (e.g., a filter). The compartment which contains thecatalyst is separated from the opening by a catalyst retention means(e.g., a filter).

EXAMPLES

[0029] The following examples are further illustrative of the presentinvention:

Example 1 Effect of Alloying Pd on Catalyst Activity

[0030] As shown in Table 1 and FIG. 1, the alloying of Pd with Pt, Ag orAu decreases the rate of deactivation (in comparison to a catalystcontaining only Pd).

[0031] Catalyst K was prepared by suspending 48.3 grams of Rhone-PoulencChemie spheralite 532, a gamma alumina containing 1.3% La₂O₃ and 0.5%Nd₂O₃ and ground to a particle size range of 75 to 212 microns, in 250ml of deionized water. To this 25 suspension was added an aqueoussolution of palladium nitrate containing 2.5 grams of Pd. The pH of thePd solution had been adjusted to 1.0 with sodium carbonate. Afterheating this suspension at 80° C. for 15 min., while maintaining the pHat approximately 6-7 with sodium carbonate, a solution of sodiumhydroxide and formaldehyde was added and the mixture stirred for another15 min. The alumina containing 4.9 wt % reduced palladium was filtered,washed with DI water, and dried overnight at 120° C.

[0032] Catalyst L was prepared by suspending 94.7 grams of Rhone-PoulencChemie spheralite 532, a gamma alumina containing 1.3% La₂O₃ and 0.5%Nd₂O₃ and ground to a particle size range of 75 to 212 microns, in 500ml of deionized water. To this suspension was added an aqueous solutionof palladium nitrate and tetrachloro auric acid. This precious metalsolution consisted of 5.0 grams of Pd and 2.0 grams of Au, and its pHhad been adjusted to 1.0 with sodium carbonate. After heating thissuspension at 80° C. for 15 min., while maintaining the pH atapproximately 9-10 with sodium carbonate, a solution of sodium hydroxideand formaldehyde was added to the mixture stirred for another 15 min.The alumina containing 4.9 wt % reduced palladium and 2.0 wt % reducedgold was filtered, washed with DI water, and dried overnight at 120° C.

[0033] Catalyst M was made in the same manner as catalyst L except thatthe final catalyst consisted of 4.9% Pd and 3.0% Au. 25 Catalyst N wasprepared by suspending 94.7 grams of Rhone-Poulenc Chemie spheralite532, a gamma alumina containing 1.3% La₂O₃ and 0.5% Nd₂O₃ and ground toa particle size range of 75 to 212 microns, in 500 ml of deionizedwater. To this suspension was added an aqueous solution of palladiumnitrate and platinum nitrate. This precious metal solution consisted of5.0 grams of Pd and 2.0 grams of Pt, and its pH had been adjusted to 1.0with sodium carbonate. After heating this suspension at 80° C. for 15min., while maintaining the pH at approximately 6-7 with sodiumcarbonate, a solution of sodium hydroxide and formaldehyde was added andthe mixture stirred for another 15 min. The alumina containing 4.9 wt %reduced palladium and 2.0 wt % reduced platinum was filtered, washedwith DI water, and dried overnight at 120° C.

[0034] Catalyst O was prepared by suspending 95.2 grams of Rhone-PoulencChemie spheralite 532, a gamma alumina containing 1.3% La₂O₃ and 0.5%Nd₂O₃ and ground to a particle size range of 75 to 212 microns, in 500ml of deionized water. To this suspension was added an aqueous solutionof palladium nitrate and silver nitrate. This precious metal solutionconsisted of 5.0 grams of Pd and 1.1 grams of Ag, and its pH had beenadjusted to 1.0 with sodium carbonate. After heating this suspension at80° C. for 15 min., while maintaining the pH at approximately 9-10 withsodium carbonate, a solution of sodium hydroxide and formaldehyde wasadded and the mixture stirred for another 15 min. The alumina containing4.9 wt % reduced palladium and 4.9 wt % reduced palladium and 1.1 wt %reduced silver was filtered, washed with DI water, and dried overnightat 120°.

[0035] Experiments were performed using catalysts K, L, M, N and O todetermine their activity and stability to generate chlorine dioxide froman aqueous solution of sodium chlorite. In these tests 50 mg portions ofthe catalyst were held in a cylindrical cell at room temperature. Anaqueous solution of sodium chlorite (150 ppm) was passed over thecatalyst at a rate of approximately 1 ml/sec. The steady stateconcentration of ClO₂ generated in the outlet stream was measured eachday over a three minute period. The concentration of ClO₂ was measuredusing an ultraviolet spectrometer in a manner known in the art. TABLE 1Effect of Alloying Pd with Pt, Ag and Au on Catalyst Activity Catalyst KL M N O Palladium, wt % 4.9 4.9 4.9 4.9 4.9 Gold, wt % — 2 3 — —Platinum, wt % — — — 2 — Silver, wt % — — — — 1.1 Support Designation532 532 532 532 532 ClO₂ Conc. (ppm): Initial 2.75 2.99 2.81 3.39 2.54Day 15 0.75 1.49 1.78 2.01 1.38 Day 30 0.4 1.03 1.55 1.32 0.94Deactivation, %: Day 15 72.7 50.2 36.7 40.7 45.7 Day 30 85.5 65.6 44.861.1 63

[0036] By substituting Cu for Au or Ag (as shown in the preparation ofcatalysts L or M or O in Table 1), comparable results are obtained.

Example 2 Effect of Different Supports on Catalyst Activity

[0037] Catalyst P was made in the same manner as catalyst K except thatthe support was Aldrich 24,338-8, a commercially available source ofMgO.

[0038] Catalyst Q was made in the same manner as catalyst L except thatthe support was Aldrich 24,338-8, a commercially available source ofMgO.

[0039] Catalyst R was made in the same manner as catalyst N except thatthe support was Aldrich 24,338-8, a commercially available source ofMgO.

[0040] Catalyst S was made in the same manner as catalyst M except thatthe support was Sturcal F, a commercially available source of CaCO₃ fromSturge Chemicals.

[0041] Catalyst T was made in the same manner as catalyst N except thatthe support was Sturcal F, a commercially available source of CaCO₃ fromSturge Chemicals.

[0042] The experiments to determine the activity and stability ofcatalysts P, Q, R, S and T for the generation of chlorine dioxide fromsodium chlorite were performed in the same manner as described above.

[0043] Table 2 describes the Mgo or CaCO₃ supports used for thiscatalytic system: TABLE 2 Example 2 Support Descriptions SupportDesignation 24,338-8 Sturcal F 532 Material MgO CaCO₃ Gamma Al₂O₃ La2O3,wt % — — 1.3 Nd2O3, wt % — — 0.5 Particle Size Range, g <200 <200 75-212Pore Volume, cc/g 1.7 E-2 1.7 E-2 7.2 E-1 Surface Area, m²/g 6.1 5.7 112

[0044] Table 3 describes the activity of these catalysts: TABLE 3 Effectof Different Supports on Catalyst Activity Catalyst P Q R S T Palladium,wt % 5 5 5 4.9 4.9 Gold, wt % — 2 — 3 — Platinum, wt % — — 2 — 2 SupportMgO MgO MgO CaCO₃ CaCO₃ ClO₂ Conc. (ppm): Initial 0.69 0.92 0.92 1.121.38 Day 15 0.29^(A) 0.72 0.89 0.98 1 Day 30 — 0.37^(B) 0.6 0.8 0.69Deactivation, %: Day 15 58.0^(A) 21.7 3.3 12.5 27.5 Day 30 — 59.8^(B)34.8 28.6 50

[0045] In comparing tables 1 and 3 it is obvious that the MgO and CaCO₃supported catalysts, when compared to those on the Rhone-Poulenc Chemiespheralite 532, have lower levels of activity, but they deactivate less.Therefore, the MgO and CaCO₃ supported catalysts would be more desirablewhen low constant levels of ClO₂ generation are needed over an extendedperiod of time. FIGS. 2, 3, and 4 show the effect of the differentsupports on the stability of the various Pd/Au, Pd/Pt, and Pd catalystsrespectively.

Example 3 The Use of K₂CO₃ Modified {fraction (1/32)}″ Alumina Spheresas a Support

[0046] Table 4 and FIG. 6 demonstrate that a suitable catalyst can alsobe made on a K₂CO₃ modified fixed bed support. A 500 gram portion of theCondea {fraction (1/32)}″ alumina spheres was modified by spraying on asolution that contained 10 g of K₂CO₃ and 215 grams of water. This wasfollowed by a drying step at 100° C. in a rotating drum and an aircalcination at 950° C. for one hour. As shown in Table 5, thismodification has no noticeable effects on physical properties of thesupport. TABLE 4 The performance of the K₂CO₃ modified {fraction(1/32)}″ alumina spheres as a catalyst support Catalyst U Palladium wt %5 Gold, wt % 3 Amount of K₂CO₃ Added, wt % 2 ClO₂ Conc. (ppm): Initial1.09 Day 13 1.09 Deactivation Day 13, % 0

[0047] TABLE 5 The effects of the K₂CO₃ modification on the physicalproperties of the {fraction (1/32)}″ alumina spheres Amount of K₂CO₃,Added, wt % 0 2 Surface Area, m²/g 97.9 95.3 Total Pore Volume, cc/g0.33 0.32 Average Pore Diameter, Å 133.5 133.7

[0048] Catalyst U was prepared by spraying 110.4 grams of the abovementioned K₂CO₃ modified Condea alumina {fraction (1/32)}″ spheres witha 28.5 ml precious metal solution containing 6 grams of palladium aspalladium chloride, 3.6 grams of gold as tetrachloroauric acid, 5ml of20% Na₂CO₃ solution. The catalyst was then reduced in a 20 ml comprisedof 29.3% sodium formate and 2% hydrazine at 25° C. for 30 minutes. Thecatalyst was then filtered, washed with DI water, and dried overnight at120° C.

[0049] The experiments to determine the activity and stability ofcatalyst U for the generation of chlorine dioxide from sodium chloritewas performed in the same manner as described in examples 1 and 2 exceptthat 0.2003 grams of catalyst U was used. The cylindrical cell used tocontain catalyst U during the experiments had the diameter of 4 mm andthe height of 19 mm, while the cylindrical cell used for the catalystsof examples 1 and 2 had the diameter of 15 mm and the height of 1 mm.

[0050] Further variations and modifications of the invention will becomeapparent to those skilled in the art from the foregoing and are intendedto be encompassed by the claims appended hereto.

[0051] U.S. Pat. Nos. 5,008,096; 4,731,192; and 4,362,707 areincorporated by reference in their entirety. Our copending U.S. patentapplication Ser. No. 08/008,971, filed on Jan. 26, 1993, is incorporatedby reference in its entirety.

What is claimed:
 1. A catalyst for producing chlorine dioxide having aslower rate of deactivation, consisting essentially of a catalystsupport selected from the group consisting of a modified supportmodified by a Group IA carbonate salt or a Group IIA carbonate salt or amagnesium salt that can be converted to MgO and a support consisting ofa Group IA carbonate salt or a Group IIA carbonate salt or a magnesiumsalt that can be converted to MgO, wherein the outside edge of saidcatalyst support is impregnated with palladium or palladium and anotherplatinum group metal or palladium and a Group IB metal.
 2. The catalystaccording to claim 1 , wherein said another platinum group metal isplatinum.
 3. The catalyst according to claim 1 , wherein said Group IBmetal is gold.
 4. The catalyst according to claim 1 , wherein saidpalladium is present in an amount of 0.1 to 20%.
 5. The catalystaccording to claim 2 , wherein said palladium and said platinum arepresent in an amount of 0.1 to 20%.
 6. The catalyst according to claim 2, wherein said palladium and said platinum are present in a ratio of Ptto Pd of 0.01:1 to 2:1.
 7. The catalyst according to claim 6 , whereinsaid palladium and said platinum are present in a ratio of Pt to Pd of0.2:1 to 0.8:1.
 8. The catalyst according to claim 3 , wherein saidpalladium and said gold is present in an amount of 0.1 to 20%.
 9. Thecatalyst according to claim 3 , wherein said palladium and said gold arepresent in a ratio of Au to Pd of 0.01:1 to 2:1.
 10. The catalystaccording to claim 9 , wherein said palladium and said gold are presentin a ratio of Au to Pd of 0.2:1 to 0.8:1.
 11. The catalyst according toclaim 1 , wherein said Group IA carbonate salt is K₂CO₃.
 12. Thecatalyst according to claim 1 , wherein said Group IA carbonate salt isCaCO₃.
 13. The catalyst according to claim 1 wherein said modifiedsupport is a formed alumina modified with K₂CO₃ present in the amount of2 to 50% by weight.
 14. The catalyst according to claim 1 wherein saidmodified support is a high surface metallic or ceramic support.
 15. Thecatalyst according to claim 14 wherein said modified support has asurface area of at least about 40 m²/g.
 16. The catalyst according toclaim 14 wherein said modified support is gamma alumina, silica-alumina,silica, or titania.
 17. The catalyst according to claim 1 , saidcatalyst produced by a method consisting essentially of preadjusting thepH of an aqueous solution of a palladium or palladium and anotherplatinum group metal or palladium and a Group IB metal salt to a pHrange of 1 to 6.3, adding said solution to a slurry of said catalystsupport and water, maintaining the pH of said slurry from 6 to 10 forseveral minutes at a temperature of 70° to 90° C., and adding a reducingagent, thereby impregnating the outside edge of said catalyst supportwith palladium or palladium and another platinum group metal orpalladium and a Group IB metal.
 18. A method of making a catalyst forproducing chlorine dioxide having a slower rate of deactivation, saidmethod consisting essentially of preadjusting the pH of an aqueoussolution of a palladium or palladium and another platinum group metal orpalladium and a Group IB metal salt to a pH range of 1 to 6.3, addingsaid solution to a slurry of water and a catalyst support selected fromthe group consisting of a modified support modified by a Group IAcarbonate salt or a Group IIA carbonate salt or a magnesium salt thatcan be converted to MgO and a support consisting of a Group IA carbonatesalt or a Group IIA carbonate salt or a magnesium salt that can beconverted to MgO, maintaining the pH of said slurry from 6 to 10 forseveral minutes at a temperature of 70° to 90° C., and adding a reducingagent, thereby impregnating the outside edge of said catalyst supportwith palladium or palladium and another platinum group metal orpalladium and a Group IB metal.
 19. A method for generating chlorinedioxide from a chlorine dioxide precursor, said method comprisingcontacting an aqueous medium containing a chlorine dioxide precursorwith a catalyst consisting essentially of a catalyst support selectedfrom the group consisting of a modified support modified by a Group IAcarbonate salt or a Group IIA carbonate salt or a magnesium salt thatcan be converted to MgO and a support consisting of a Group IA carbonatesalt or a Group IIA carbonate salt or a magnesium salt that can beconverted to MgO, wherein the outside edge of said catalyst support isimpregnated with palladium or palladium and another platinum group metalor palladium and a Group IB metal.
 20. The method according to claim 19wherein the temperature is 5° to 80° C.
 21. The method according toclaim 20 wherein the temperature is 5° to 50° C.
 22. The methodaccording to claim 19 wherein the pH of said aqueous medium is 1 to 8.23. The method according to claim 22 wherein the pH is from 4 to
 8. 24.The method according to claim 19 wherein the time of the contact betweensaid catalyst and said chlorine dioxide precursor ranges from 0.01 to 20seconds.
 25. The method according to claim 19 wherein said chlorinedioxide is contacted with contact lenses for disinfecting.
 26. A twocomponent package comprising the catalyst according to claim 1 and achlorine dioxide precursor.
 27. A method for generating chlorine dioxidefrom a chlorine dioxide precursor comprising providing amulticompartment container, a first compartment containing a chlorinedioxide precursor, a second compartment containing the catalystaccording to claim 1 , dispelling from said first compartment a quantityof said chlorine dioxide precursor to flow into said second compartmentcontaining said catalyst, contacting said precursor with said catalystthereby forming chlorine dioxide, and ejecting said chlorine dioxidefrom said container to the surface of an item to be disinfected ortreated.